The best design system we ever shipped wasn't the most beautiful one — it was the one developers actually used without being asked twice. That's the real test: does it get adopted, or does it get quietly ignored the first time someone's in a hurry?
We start every design system with tokens, not components. Color, spacing, typography and radius get defined once, referenced everywhere, and changed in exactly one place when the brand evolves. Components come second, built strictly from those tokens so visual drift becomes structurally difficult.
The other habit that matters more than people expect: documenting the "why", not just the "what". A button component with five variants is useless if nobody remembers which variant is for which situation six months later.
Scale isn't about having more components — it's about having fewer decisions left to make on any given day.